The present invention relates generally to Magnetic Resonance Imaging (MRI) systems, and more particularly, to a method and system for improving transient noise detection.
Magnetic Resonance Imaging (MRI) is a well-known medical procedure for obtaining detailed, one, two and three-dimensional images of patients, using the methodology of nuclear magnetic resonance (NMR). MRI is well suited to the visualization of soft tissues and is primarily used for diagnosing disease pathologies and internal injuries.
Typical MR systems include a superconducting magnet capable of generating a strong, homogenous magnetic field around a patient or portion of the patient; a radio-frequency (RF) transmitter and receiver system, including transmitter and receiver coils, also surrounding or impinging upon a portion of the patient; a magnetic gradient coil system also surrounding a portion of the patient; and a computer processing/imaging system, receiving the signals from the receiver coil and processing the signals into interpretable data, such as visual images.
The superconducting magnet is used in conjunction with a magnetic gradient coil assembly, which is temporally pulsed to generate a sequence of controlled gradients in the main magnetic field during a MR system data gathering sequence.
MRI systems are sensitive to RF signals including the desired signal from the patient, as well as any undesired RF noise energy. A class of RF noise energy, commonly referred to as transient or xe2x80x9cspikexe2x80x9d noise, has origins as a triboelectric phenomena.
Triboelectricity results when two materials are in contact with one another and are subsequently separated. Vibration introduced into the system through gradient coil operation usually provides the mechanical movement necessary for intermittent contacts and triboelectric events. Charge transfer (or static electricity) imbalances build up and eventually result in an electric discharge. This discharge generally occurs very rapidly and with significant (though short duration) current flow, and a broadband RF radiation results. This RF noise energy, when coupled into the MR system input, tends to result in distorting image artifacts.
A Transient Noise Filter is typically provided to reduce the impact of the aforementioned artifact. Current Transient Noise Filters, however, have performance shortcomings, such as using MR signals to sense noise events.
For example, current MR systems attempt to sense transient noise events on the incoming receive signal line. At this point in system operation, the broadband RF noise energy has been substantially shaped by the system coil, receive filters, and preamplifier characteristics. Consequently, the remaining energy is not easily separable from the desired MR information using current technology.
Using an incoming MR signal to sense a noise event also requires that the MR signal be delayed for activation of remedial measures. This delay function limits the bandwidth of the MR signaling path and degrades the phase and frequency performance of the MR signal. Therefore, the effectiveness of current implementations is inherently limited.
The disadvantages associated with current MR systems have made it apparent that a new technique for transient noise detection is needed. The new technique should detect transient noise independent of the MR signal and should not be dependent on the field strength of the scanner or scanner mode. The present invention is directed to these ends.
In accordance with one aspect of the present invention, a transient noise detection system includes an imaging system including a magnetic field coil and an imaging bore. The imaging system is adapted to generate an imaging signal through a signal cable, wherein the imaging signal is corruptible by a noise event. A noise event detector is positioned outside of the imaging bore and proximate to the signal cable and is adapted to detect the noise event. The noise event detector is also adapted to generate a sensed noise signal.
In accordance with another aspect of the present invention, a method for transient noise detection for an MR system having a magnet bore includes generating an MR image signal wherein the MR image signal is corrupted by noise, detecting the noise within the MR image signal external to the magnet bore, generating a detected noise signal, and correcting the MR signal of the detected noise signal.
One advantage of the present invention is that detection of transient noise independent of the MR signal preserves full MR signal clarity. Furthermore, the present method is not dependent on scanner field strength or scanner mode.
The present invention, together with attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying FIGURES.